1. Field of the Invention
The present invention relates to a fibrous web such as paper and non-woven fabrics having a high water containability, and a process for producing the same, specifically relates to a fibrous web having a high water containability which is highly safe in use, soft and excellent in feel to skin, and lints little web waste in its producing process, as well as is suitable for food, sanitary and household products.
2. Description of the Related Art
In the household paper such as tissue paper and toilet tissue and other fibrous web, the softening agents have been used occasionally in order to, for example, soften their feel.
The softening agent acts not only as a plasticizer of a wet strength-reinforcing agent for paper (i.e., a chemical agent to maintain the strength of paper at wet condition), but also as follows.
That is, in such softening agents have hydrophilic groups and lipophilic groups, and the hydrophilic groups are adsorbed to cellulose, whereas the lipophilic groups orient outside of the cellulose. Accordingly, the cellulose becomes surrounded with the lipophilic groups, resulting in flexibility as well as smoothness of the surface. Furthermore, the smoothness between cellulose becomes good and the resistance between cellulose becomes less, and consequently, the feel to skin becomes smooth and soft. In this state, the hydrogen bonds in the fiber are sealed and the smoothness between fibers are enhanced to make the feel soft.
The softening agents having above-mentioned activities may be applied by mixed with the above-mentioned raw materials of fibrous web such as tissue paper to web-make, or by impregnating to web which is wet, i.e., after the web formation and before drying, or web which is obtained after web-making and before drying (hereinafter, referred to as the external addition method).
As to the softening agent, there have been known, for example, surfactants, wax emulsions (i.e., those which are obtained by emulsifying waxes with surfactants and in which the waxes act as the above-mentioned lipophilic groups), and reactive softening agents (i.e., those which react with cellulose strongly and make aliphatic hydrocarbons orient surrounding fibers regularly).
In addition, recently, a silicone-based softening agent has been developed in order to give tissue paper a soft, silky and flannel-like tactile feel as well as high bulk property (referred to Japanese Patent Application Laid-open Nos. 224626/1990 and 900/1991).
On the other hand, fibrous webs used for food, sanitary and household products are required to be highly safe in use, since they should contact with food, mucosa, skin, and the like.
However, the conventional softening agents described above are chemically synthesized products, and there is some fear in safety of the webs to which such softening agents are applied to the webs in high concentration.
As mentioned above, the conventional softening mechanism consists in the inhibition of hydrogen bond formation between fibers, in which the lipophilic groups of the softening agent orient outside of cellulose, and the hydrophilic groups are adsorbed on the cellulose. Accordingly, the interlacing or binding of fibers are impaired and the some fibers fall out, resulting in increase of linting of web waste such as paper edge dust and fiber dust.
Further, the lipophilic groups orienting outside of cellulose provide the fiber a water repellency, and impair its water adsorption property. Therefore, the water adsorption property essentially needed to tissue paper, toilet tissues, etc. made of such fibers is also impaired.
According to the above problems, the conventional softening agents have been limited in the amount to be applied to fibrous webs, and can not provide an excellent softness with the resulting fibrous webs such as tissue paper and toilet tissues.